Concrete used in various industries for architectural structures, foundations, walls, pavements, bridges, highways, parking structures, reservoirs, dams, pipes, footings, fences, poles, boats and other structures is often exposed to vapor, mist or liquid sulfuric acid and H2S. The use of specialized industrial (film forming) coatings is the most common method for protecting concrete against the destructive action of sulfuric acid. Other methods for protection include the application of certain silicates, such as potassium silicate (dry gunning).
Unfortunately, coating failure occurs rather frequently in the relevant industries, which can lead to very rapidly progressing damage to the concrete. The life expectancy of specialized acid resistant coatings such as epoxies, vinyl esters, and polyurethanes has proven to be substantially less than adequate, which necessitates removal of the failed coatings and re-application of new coatings. However, unless salts, and especially sulfate salts, are removed from the surface and sub-surface areas of the concrete, new coatings will tend to fail, and damage to the concrete will continue to develop. In most cases, the surface of the concrete is treated by at least one of water blasting and treatment with one or more complexing agents. However, water blasting or treatment with most of the currently known complexing agents will not provide sufficient salt removal, and re-coating is often once more required after a very short time.
Others have previously put forth effort in scale removal or prevention technologies. For example, U.S. Pat. No. 3,688,829 to Jones describes a process for removing scale from an oil well using an aqueous solution of gluconates and hydroxides of alkali metals at a weight ratio between 2:1 and 5:1 at a concentration of the combination between 10 to 30% by weight. However such known compositions and processes were used in a different field and contemplate only solutions having low ratios of gluconate to KOH, which operate only at relatively low concentrations of the gluconate/KOH mix.
All publications identified herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Further examples of known efforts can be found in U.S. Pat. No. 3,793,209 to Thompson, which describes an emulsion composition comprising ethylenediaminetetraacetic acid salt, sodium citrate or potassium glycolate as a calcium sulfate scale solvent; U.S. Pat. No. 5,932,019 to Espinoza et al., which describes a method for minimizing calcium sulfate dehydrate on a tool by contacting the tool with a solution comprising a non-calcium phosphate, water and a pH modifier (e.g., citric acid); U.S. Pat. No. 6,761,774 to Ellis et al., which describes a composition and method for in situ removal of scale using a composition comprising an alkali metal hydroxide basic agent and a chelating agent having at least two carboxylic acid functional groups (e.g., citric acid); International Patent Application Publication Number WO 87/04143 to Abadi, which describes a scale removal composition comprising an aliphatic alpha-hydroxy carboxylic acid, a gum or polymer soluble in water at a pH of 3 or less, water, and optional sodium silicate; and U.S. Pat. No. 3,639,279 to Gardner et al., which describes a scale removal composition that comprises a salt of diglycolic acid, an alkali metal hydroxide and optionally gluconic acid or a salt thereof.
Unfortunately, the aforementioned known compositions are insufficient to effectively remove acid calcium salts such as gypsum from the surface of concrete, and especially from below the surface.
Therefore, even though some methods and compositions are known in the art to help remove scale from cementitious materials, all or almost all of them suffer from one or more disadvantages. Thus, there is still a need to provide improved compositions and methods, especially when re-coating of concrete in service is performed, in addition to or as alternative to traditional media or water blasting to allow for effective removal of salts and particularly sulfate salts.